When a vessel moves at the surface of a water mass, a number of different resistance factors act against the vessel's movement. The resistance coefficients for the individual components for a displacement vessel are illustrated in FIG. 1. As can be seen, the frictional resistance CF and the wave resistance CW are the two major factors. For a given vessel, Froude's number [FN] increases with increasing speed, indicated along the x-axis:
                              F          N                =                              Speed            ⁡                          [                              m                s                            ]                                                                          9.81                ⁡                                  [                                      m                                          s                      2                                                        ]                                            ×              length              ⁢                                                          ⁢              of              ⁢                                                          ⁢                              vessel                ⁡                                  [                  m                  ]                                                                                        (        1        )            
The resistance coefficients CF and CW are multiplied by the square of the speed (v2) to obtain the resistance to forward movement in Newtons [N]. Consequently, the wave resistance increases very rapidly with increasing speed.
Most vessels have a bow configuration where the water masses the vessel meets when at speed are essentially displaced laterally in the transverse direction of the vessel. As the vessel moves through the water masses, a local deceleration of the water is produced ahead of the bow, i.e., a reduction of relative water velocity relative to the hull. Further back, where the width of the hull increases, a relative acceleration of the water masses occurs, as the water is forced out to the sides, and possibly under the vessel, as a consequence of the shape of the hull. These relative changes in water velocity are the origin of wave formation and change in pressure, and are given by Bernoulli's equation:½ρν2+ρgh+p=constant  (2)
Lower relative water velocity leads to an increase in pressure and a wave crest in relation to the surrounding water masses, whilst higher relative water velocity gives lower pressure and a wave trough.
A vessel thus forms a wave crest ahead of the vessel, where the relative water velocity is low. Further back, where the width of the hull increases, a wave trough is produced due to high relative water velocity.
The increased water velocity under the hull also results in lower pressure under the hull, and consequently loss of buoyancy when the vessel's speed increases. This resistance is included in the term wave resistance.
The waves generated by a hull in motion, and which spread to surrounding water masses, represent lost energy. The percentage of the total resistance to forward movement at sustained speed that wave resistance normally constitutes is, depending on vessel type, 30-70%, and increases sharply with increasing speed.
To reduce a vessel's resistance to forward movement, it is therefore crucial to minimise wave resistance.